The invention relates to a method for processing vegetable, fruit and garden waste, indicated briefly as VFG-waste, in which the waste is brought into a washing-separating device and is divided into two fractions with the help of water.
Such a method is known from the German patent 811.821. Therein, a separation of the waste into fractions of different densities takes place in that the fraction with the lowest density will end up floating on the water. This fraction is removed from the surface of the water and will substantially consist of organic material. The remaining fraction will substantially consist of sand and similar materials.
After the material of low density has been removed from the water used for washing, the water will contain dissolved and colloidally divided fractions, particularly salts, well-soluble nutrients and various acids. Thus, it will have to be cleaned before it can be re-used or drained. Further, it has appeared that the heavy metals nearly always present in VFG-waste, will substantially adhere to the finer particles and thus partially end up in the separated organic material, since this will contain both coarse and fine particles.
In further processing of the organic material, two different methods, namely aerobic composting and anaerobic fermentation, are applied in practice.
The difficulty of composting lies mainly in the fact that many odours arise, and of fermentation in the fact that it requires a considerable investment in equipment and is therefore an expensive process, although one can obtain biogas by it. It will also be appreciated that in both cases heavy metals can be present in the final material.